1. Field of the Invention
The present invention relates to a method of consolidating geological formations, this method being more particularly applicable to reservoirs containing oil or gas for eliminating the infiltration of sand into the wells passing through sandy formations which are little or not at all consolidated. Generally, this method may be used for locally consolidating permeable formations.
2. Description of the Prior Art
Different methods have already been proposed for preventing the infiltration of sand into new wells, or for treating wells giving rise to sand infiltration during working of the oil or gas deposits.
A first type of method consists in retaining the sand by mechanical means, using artificial screens with calibrated orifices, or piles of gravel having a well defined granulometric distribution, depending on the dimension of the grains of sand of the geological formation through which the well passes. Such a method, delicate to implement, is often used for equipping new wells.
A second type of method consists in injecting into the geological formation a liquid resin which, by polymerizing, creates a bond between the grains of sand. The efficiency of a chemical method of this second type is uncertain, for the polymerization reaction of the resin injected depends essentially on the conditions reigning in the well at the level of the formation and on the characteristics of this formation. Such a method therefore does not allow the degree of advance of a chemical reaction to be controlled. The result is the risk either of insufficient consolidation of the formation, if the degree of polymerization of the resin is too low, or too great a reduction of the permeability or even complete clogging of the geological formation, if too much polymer is retained in certain pores.
To overcome this problem, the French patent No. 2 474 558 describes a method in which the polymerization reaction takes place between a liquid chemical agent containing appropriate catalysts placed about the well to be treated and an injected oxidizing gas.
The flow of the gas after positioning the polymerizable agent ensures that permeability is maintained. The liquid organic mixture contains a polyethylene compound and a catalyst such that the oxidizing polymerization reactions lead to the consolidation of the medium without it being necessary to preheat the formation.
However, this method requires the use of an oxygen-inert gas mixture whose availability is not always evident. In addition, the amount of oxidizing gas must be limited so that, following release of the heat by the oxidization reaction, the temperature does not reach values higher than 350.degree. C., at which the polymerized product would be degraded by combustion.